convert admonition to MyST admonitions

Mapping (per ADR 0002):
  {{< admonition warning >}}…{{< /admonition >}}  →  :::{warning}…:::
  {{< admonition note >}}…{{< /admonition >}}     →  :::{note}…:::

Author: lundybernard

content/community/onboarding.md

@@ -2,9 +2,9 @@
 title: "Onboarding"
 ---
 
-{{< admonition warning >}}
+:::{warning}
 This is a draft document.
-{{< /admonition >}}
+:::
 
 - Organizing sprints
   - Organising sprints are an excellent way to invite new collaborators, solve issues, gather contributions and broaden the project community. Some helpful tips for organising a sprint efficiently:

content/contributors/first-contribution.md

@@ -113,7 +113,7 @@ git push -u origin [BRANCH NAME]
 
 Enter your GitHub username and password if requested.
 
-{{< admonition note >}}
+:::{note}
 Entering your username and password every time you run `git push` can get tedious!
 Luckily GitHub lets you use an SSH key to authenticate automatically.
 Basically this involves creating two special files: one kept secret on your computer, and one uploaded to GitHub. If you want to set that up, see here:
@@ -123,7 +123,7 @@ Basically this involves creating two special files: one kept secret on your comp
 
 You can also set up an SSH key using the `gh` command-line tool: https://cli.github.com/manual/ if you prefer.
 Mac and Windows users (but not Linux users!) who prefer to use `git` through a GUI can manage authentication using the [GitHub Desktop app](https://desktop.github.com/).
-{{< /admonition >}}
+:::
 
 ### Step 9: Open PR
 

content/maintainers/index.md

@@ -2,9 +2,9 @@
 title: "Maintainers"
 ---
 
-{{< admonition warning >}}
+:::{warning}
 This is a draft document.
-{{< /admonition >}}
+:::
 
 The scientific Python ecosystem welcomes your expertise and enthusiasm!
 

content/maintainers/interacting-with-new-contributors.md

@@ -3,9 +3,9 @@ title: "How to interact with new community
 members"
 ---
 
-{{< admonition warning >}}
+:::{warning}
 This is a draft document.
-{{< /admonition >}}
+:::
 
 As a maintainer, you will be the first point of
 contact for new community members. It is important

content/maintainers/managing-conflict.md

@@ -2,9 +2,9 @@
 title: "Managing conflict"
 ---
 
-{{< admonition warning >}}
+:::{warning}
 This is a draft document.
-{{< /admonition >}}
+:::
 
 ### Code of Conduct
 

content/maintainers/meeting_types.md

@@ -2,9 +2,9 @@
 title: "Meeting types"
 ---
 
-{{< admonition warning >}}
+:::{warning}
 This is a draft document.
-{{< /admonition >}}
+:::
 
 With growth and sustainability in mind, every OSS project would benefit from holding the following recurring meetings: